On the Roles of Cellulose Nanocrystals in Fiber Cement: Implications for Rheology, Hydration Kinetics, and Mechanical Properties

Fiber cement reinforced with pulp fibers is one of thekey driversfor the decarbonization of nonstructural building materials, wherethe inclusion of sustainable pulp fibers at high proportions (i.e.,> 8 wt %) renders poor workability of fiber-cement slurry witha concomitantloss in mechanical strength. Petrochemical-derived superplasticizers,i.e., polycarboxylates (PCEs), are predominantly used in fiber cement(including cement mortars) because they dramatically improve (content<0.5 wt %) the slurry rheology but reduce the rate of hydrationand weaken the strength of the cured composite. Thus, it is crucialto explore renewable and bio-based superplasticizers devoid of anynegative traits (if possible) of the conventional PCEs. In this study,we examined wood-derived cellulose nanocrystals (CNCs) as a multifunctionaladditive in fiber cement (bleached pulp fiber content: 8 wt %). Infiber cement, variation of the content (0.02-4 wt %) of CNCsresulted in improvement in the shear thinning behavior of the fiber-cementslurry and thereafter increased the hydration kinetics at high CNCcontents (2-4 wt %). Notably, the flexural strength of thecomposite also exhibited improvement upon the addition of CNCs; themaximum strength was observed at 4 wt % of CNCs. Overall, the beneficialroles of CNCs afforded >10 wt % (in-total) bio-based content infibercement without compromising the mechanical strength and curing time(compared to PCEs); hence, the findings of this study could unravelnew avenues in interface engineering of cement composites leveragingthe multifunctional features of biomaterials, thus enhancing sustainability. Cellulose nanocrystals as a green andsustainable additivefor cement composites modify rheology, accelerate hydration kinetics,and improve mechanical properties.